The present invention relates in general to radiotelephone communication systems, and more particularly to a method for a radiotelephone to scan for alternate radiotelephone systems.
As various different types of communication systems have arisen for radiotelephones, it has become beneficial to provide portable and mobile radiotelephone stations that are interoperable between these various communication systems. As a first step, dual-mode phones have been developed that can operate between two radiotelephone systems. For example, the ANSI-136 time division multiple access (TDMA) and GSM (Global System for Mobile Communications) communication systems are intended to work together in the same mobile terminal equipment, as described by the GSM/ANSI-136 Inter operability Team (GAIT) specification, GSM/ANSI-136 Common Mobile Terminal Specificationxe2x80x94Baseline Text, Revision 3; GSM/ANSI-136 Inter operability Team (GAIT); Oct. 26, 1999, wherein a mobile radiotelephone is required to scan for alternate technologies. However, no mechanisms are given to do this without service interruptions on the selected technology and no exception cases are described.
The definition of a GAIT mobile station permits a single mobile station to automatically determine the availability of alternate radio access technologies, and thus obtain service on the most desirable radio access technology available in a given location. In particular, the GAIT specifications allow for a mobile station to perform (background) scans of radio access technologies other than the one on which it has currently obtained service. However, there are some system performance issues that degrade the intended behavior of the mobile station on the selected network while these scans of alternate technologies are in progress. Specifically, when a mobile station is operating as a GAIT compliant handset, and has obtained service on a GSM-based (900 MHz, 1800 MHz or 1900 MHz) network, the scan of ANSI-136 technology cannot be done without missing paging messages from the GSM network. This results in a waste of GSM network resources for paging, and unpredictable mobile paging response behavior. In the existing GAIT specifications, there is no mechanism to allow the mobile to perform the alternate technology scans without compromising operation on the GSM network. As a result, a base station sending such paging messages, and receiving no reply in return, may presume that the mobile has been turned off and remove the unit from its active list. The mobile unit, when trying to resume communications will need to reestablish the connection with the base station, wasting time and resources. Also, missing GSM pages wastes resources and has been perceived by operators as providing unpredictable service.
In addition, there is an issue with a standards conflict. For an mobile unit camped onto a GSM network, xe2x80x9cThe MS is required to attempt to decode a message every time its paging subchannel is sentxe2x80x9d per GSM 05.08, xe2x80x9cDigital cellular telecommunications system (Phase 2+); Radio Subsystem Link Controlxe2x80x9d, European Telecommunications Standards Institute (ETSI), European Standard (Telecommunications series), v6.7.1, sec. 6.5. However, there is a fundamental contradiction between this and the GAIT specifications, which state that background scans are required, and are to be done xe2x80x9cin such a way as to minimize interruptions in the mobile station""s monitoring for pagesxe2x80x9d per GSM/ANSI-136 Common Mobile Terminal Specificationxe2x80x94Baseline Text, Revision 3; GSM/ANSI-136 Inter operability Team (GAIT); Oct. 26, 1999, sec. 6.2. One way to address this issue is to use a dual-receiver mobile unit. However this is cost prohibitive due to the additional hardware and processor requirements.
Therefore, the need exists for a method to allow a mobile unit to perform alternate radiotelephone system scans without missing paging messages on the system where it is presently camped. Additionally, it would prove beneficial to provide this performance improvement with relatively simple hardware and software and with little or no additional cost.